A 2010 study in the Proceedings of the National Academy of Sciences compared the microbiots of children living in rural Burkina Faso in West Africa to the microbiots of urban, city-dwelling children in Italy. The African children ate a high-fibre diet of vegetables, grains and legumes, with no processed foods, whereas the diet of the European children was full of sugars, animal fats and refined grains. The gut microbes of the children from Burkina Faso were very different from — and much more diverse than — those of the Italian kids.We wouldn’t want to say that children in Burkina Faso have a healthier lifestyle than Italian children. They are more likely to suffer severe infections and malnutrition, and they have a lower life expectancy than children born in Western Europe. But they also have a decreased risk of suffering from the immune diseases that are epidemic in the Western world.In an ideal world, children would harbour a rich and diverse community of microbes without the threat of severe infectious diseases, but our current practices only address half of this equation. Given how well bacteria respond to diet, eating a variety of foods is perhaps the best way to increase microbial diversity, and there’s no better time to do this than during the first few years of life.As a practical matter, this means that we shouldn’t feed a baby only rice cereal for weeks until the package is finished. We should offer a variety of grains, including oats, rice, barley and quinoa. It’s also important to offer whole grains instead of refined ones. The Western diet is extremely low in fibre, and refined grains contain very little of it.Protein-rich legumes, such as lentils, beans and peas, have an abundance of fibre and can be easily mashed for babies. Also try non-traditional starchy vegetables such as sweet potatoes, parsnips or cassava (tapioca) rather than just sticking to low-fibre veggies such as potatoes. For older children, add fermented foods, such as yoghurt, kefir, sauerkraut and other pickled vegetables.